The present invention relates generally to an antenna, and more particularly to a multi-frequency band antenna for use in a wireless communication device.
In recent years, personal wireless communication devices have become increasingly popular. To provide consumers with a wireless communication service of multiple functions, the design of cellular phone modules operating in two or more frequency bands is gaining popularity. Thus, there exists a need for an antenna, which is responsible for transmitting and receiving signals, capable of operating in two or more frequency bands.
Antennas are generally divided into hidden and non-hidden types by their appearance. Most non-hidden type antennas are made by an antenna structure comprising a wire antenna element and a helix antenna element in order to operate in two frequency bands. U.S. Pat. No. 6,054,966 discloses an antenna structure with at least two resonance frequency bands. As shown in FIGS. 1a and 1b, the antenna structure 100 comprises a first antenna element (P2 or P3) which is preferably a straight conductor, and a second antenna element (HX3 or HX4) which is preferably a conductor wound into a cylindrical coil, with the two antenna elements having different resonance frequencies. The rod element (P2 or P3) is partly inside the other antenna element (HX3 or HX4) and they may comprise a same feed point A4 or separate feed points A5 and A6. The antenna structure may also comprise a third antenna element (not shown in FIGS. 1a and 1b) which is preferably a conductor wound into a cylindrical coil comprising a different resonance frequency from those of the other two antenna elements.
The antenna structure disclosed in the U.S. patent is widely used in a mobile phone operating(, in at least two cellular telephone systems using different frequencies. However, such an antenna needs to be assembled in such a way that it is extendable out of the device case, and the extended antenna may easily be broken or damaged due to user""s carelessness.
Hidden type antennas are mainly designed in accordance with the principle of a planar inverted F-antenna. U.S. Pat. No. 5,926,139 discloses a single planar antenna for use in two frequency bands. As shown in FIG. 2, the planar antenna includes a first radiating portion 202 and a second radiating portion 204. The two radiating portions for the two bands are joined by the connecting portion 208 of a conductive layer 206 and spaced from the ground plane 210 of the conductive layer 206. Each radiating portion is formed as a planar inverted F-antenna on the conductive layer 206. The conductive layer is preferably a metallic layer. A grounding pin 212 interconnects the connecting portion 208 and the ground plane 210 and a single feed pin 214 connects the connecting portion 208 to the input/output port of a transceiver circuitry.
The planar antenna is designed by forming a slit on a planar patch in order to operate in both of the desired frequency bands. However, such an antenna has a drawback that its operable frequency bandwidth reduces as the size of the planar patch is reduced. Therefore, the antenna may only operate in a smaller frequency range to compromise with the small size.
The present invention has been made to overcome the above-mentioned drawbacks of a conventional antenna. The primary object of the invention is to provide an antenna operable in multiple frequency bands used in a personal wireless communication device. The multi-frequency band antenna comprises a first radiating element, a second radiating element, and a feed radiating element. The first radiating element made of a conductive material is shaped as an extended bent wire to function as an antenna element for a first frequency band to control the characteristics of the first frequency band. The second radiating element also made of a conductive material functions as an antenna element for a second frequency band to control the characteristics of the second frequency band.
The multi-frequency band antenna comprises a feed radiating element having at least two ends. One end is used as a signal feed point so that the first frequency signal and the second frequency signal can share a same signal feed point. The other end electrically connects the first radiating element to the second radiating element to form a top loaded structure. According to the invention, the multi-frequency band antenna uses the top loaded structure as well as the design of the extended bent wire antenna to achieve two resonance frequencies, wide frequency bands and the hidden nature.
The object of the design of the extended bent wire antenna is to effectively reduce the overall length of the antenna. The object of the top loaded structure is to change the antenna""s extension direction so that the antenna can be completely placed and hidden in the case of a mobile phone. In addition, low cost is another object of the multi-frequency band antenna of the invention. Because the antenna can be fabricated by popular materials, the material and manufacturing cost can thus be reduced substantially. It is very suitable for mass production and is highly competitive in the market.
In the preferred embodiments of the invention, the first radiating element uses an extended bent wire with an extended square-wave pattern, an extended saw-tooth pattern, an extended sinusoid pattern or combinations of those patterns. It is used to control the characteristics of the lower frequency band of the antenna and to reduce the overall length. The central frequency and the bandwidth of the antenna can be adjusted by controlling the length of the bent metal wire and the number of bends. The second radiating element is a straight conductor. It is used to control the characteristics of the higher frequency band of the antenna. The central frequency and the bandwidth of the higher frequency band of the antenna can be adjusted by controlling the length and the width of the straight conductor. This straight metal wire can be implemented with extended bent patterns.
The feed radiating element has three preferred embodiments according to the invention. One embodiment is a metal wire without a base. Another two embodiments are metal wires with a base. The metal wires are respectively placed on the top surface and in the interior of the base. Similarly, the two radiating elements also have three preferred embodiments. One embodiment is two metal wires without a base. Another two embodiments are two metal wires with a base. Metal wires are respectively placed on the top surface and in the interior of the base and can be distributed in different layers. The surface for placing the metal wires can be a plane or a curved surface.
The invention uses a two-frequency band antenna and a commercial three-frequency band antenna to analyze the measurement results of the return loss of the multi-frequency band antenna of the invention. The operating range of the two-frequency band antenna is designed in GSM 900 and DCS 1800 frequency bands. The bandwidths at xe2x88x9210 dB are 130 MHz and 230 MHz, respectively. The higher frequency range of the commercial three-frequency band antenna can include DCS 1800 and PCS 1900 frequency bands.
The foregoing and other objects, features, aspects and advantages of the present invention will become better understood from a careful reading of a detailed description provide(l herein below with appropriate reference to the accompanying drawings.